When I turn the switch to lock the differential they no longer lock. First the rear wouldnt lock, and now the front wont lock. Does the Bently manual give a procedure for troubleshooting these? Also, where can you get parts for them? I looked several places online and no one listes parts for the locking differentials.
Thanks

Your vacum switch is probably bad. Cheap part, but can be a hard fix due to location of switch.

Check the vacuum on the lines to the actuators on the diffs, my guess is that the lines themselves could be shot. You can add vacuum to the actuators themselves and see if they work.

I've read that others have moved to electrically operated actuators instead. I can't imagine that it would be difficult to do.

Bob D'amato has done these to his 4kq and Urq. I think he just used generic parts to do so. Do a search on the audifans site's archives. He seemed to imply that it wasn't that hard to do.

I didn't take notes at the time, since my 4kq's worked. That and it was SUCH a POS that it wasn't worth whatever manual labour exerted to fix or improve on it!

My '84 is all vacuum and both locks were acting up. I went under the car and replaced all the hose sections around the rear servo mechanism. I think there was about 4-5 separate lines from 6-12 inches in length that solved the problem. Also, check the lines under the hood around the distributor and A/C plumbing.